1. Field of the Invention
The present invention relates to a receiver and a receiving system that can receive analog radio broadcasting.
2. Background Art
FM signals used in analog radio broadcasting have a constant envelope. However, when FM signals propagate through multiple paths, the constant envelope of the FM signals may be lost because of the multipath effect.
The constant modulus algorithm (CMA) is an equalization algorithm based on the constant envelope of the FM signals. The CMA is expressed by the following update formula (1), where “x” represents an input signal, “y” represents an output signal, “w” represents a weight, “μ” represents a step coefficient, and “σ” represents a target amplitude.w(n+1)=w(n)−μx(n)y*(y2−σ2)  (1)
In the above formula (1), the output signal “y” converges to the target amplitude “σ”. Therefore, the CMA algorithm effectively reduces multipath to keep the output having a constant envelope.
For example, there is a conventional receiving system for in-band on-channel (IBOC) hybrid digital radio (HD-Radio). The receiving system uses a spatial equalizer using two antennas and two tuners, for example.
For a conventional spatial equalizer, when the tuners use filters having different pass bands, such as when one of the tuners uses a filter for IBOC, and the other uses a filter for FM, a difference in delay time can occur between the two tuners. The difference in delay time reduces the effect of multipath equalization by the spatial equalizer.
There is a conventional receiver that has delaying means that delays the signal received at one antenna with respect to the signal received at the other antenna (see Japanese Patent Laid-Open No. 6-169273, for example)
The conventional receiver described above is intended to reduce the possibility of destructive interference between signals input at two antennas.
However, the conventional receiver described above does not take into account the effect of the difference in delay time on the effect of multipath equalization by the spatial equalizer.